Materials feeders typically include a bowl in which material is contained. A rotating feed screw which passes through the bowl feeds the material in metered quantities through an opening at the bottom of the bowl to utilization equipment.
It is important to seal the opening in the bowl through which the feed screw passes to avoid escape of material, particularly abrasive and floodable materials, contained in the bowl. Among the criteria for sealing units in such an application are:
(1) acceptable for feeding solids and powders such as food products, extremely abrasive materials and extremely free-flowing materials, PA1 (2) compatible with materials feeders already in use, PA1 (3) quick and easy feed screw replacement, PA1 (4) sealing must be effected without lubrication, and PA1 (5) operation at temperatures below 140.degree. F.
Various commercially available sealing units fail to provide seals which sufficiently contain the materials in the bowl. The main factors which cause leakage of material through a faulty sealing unit are the head load of the material in the bowl and an extension hopper positioned above the bowl, and the forces resulting from the agitation of the material.
Among the problems with commercially available sealing units are the inability to compensate for eccentricity of the feed screw hub and eccentric feed screw rotation due to the weight of the feed screw. Another problem is that the lips of the sealing unit can be damaged as the feed screw is inserted for passage through the sealing unit. In addition, failures of the sealing unit can occur because of the heat caused by the contact surfaces of the lips of the sealing unit, in some applications reaching 200 degrees F.